The present invention relates to a method of making a spark plug.
A number of spark plugs of the kind in which a noble metal tip made of a metal containing Pt, Ir or the like as a major component is welded to an end of an electrode in order to improve the resistance to spark consumption have heretofore been proposed. Since a center electrode side whose polarity is frequently set negative at the time of spark discharge is subjected to strong attack of spark and liable to be consumed, a noble metal chip can produce a striking effect when used in the center electrode. However, as application of such spark plugs to high-output engines or lean-bum engines increases, a noble metal chip is employed increasingly also in the ground electrode side so as to meet the requirement that the ground electrode side has a high resistance to spark consumption. Heretofore, the noble metal chip on the ground electrode side is made of a Pt system alloy and welded to a main body of the ground electrode made of a Ni alloy or the like.